1. Field of the Invention
The present invention relates to a resin multilayer substrate including a signal line and preferably for use in a bent state, and an electronic apparatus including the resin multilayer substrate.
2. Description of the Related Art
Examples of resin multilayer substrates made of thermoplastic resin include a flexible substrate on which components are densely mounted in an electronic apparatus or the like and a flat cable arranged so as to extend through small gaps or the like in an apparatus. Such a resin multilayer substrate may include a triplate line as a signal line for transmitting high-frequency signals. The triplate line is a signal line including a line conductor and grounding conductors disposed in the resin multilayer substrate such that both surfaces of the line conductor oppose the corresponding grounding conductors, which are wider than the line conductor (see, for example, Japanese Unexamined Patent Application Publication No. 2011-71403). Since the grounding conductors are provided at both sides of the triplate line, the triplate line is resistant to external noise, and unnecessary radiation (i.e., unnecessary emission) does not easily occur.
There has been an increasing demand for smaller and thinner electronic apparatuses, such as mobile devices, and spaces in such an apparatus are required to be utilized efficiently. In a mobile device, for example, the resin multilayer substrate may be bent so as to follow the shape of the space in the device. However, in the case where the resin multilayer substrate includes the triplate line, the two grounding conductors included in the triplate line overlap and cannot be easily deformed. Therefore, it is difficult to bend the resin multilayer substrate. When the resin multilayer substrate including the triplate line is forcibly bent, one of the two grounding conductors tries to expand and become longer than the other grounding conductor. Accordingly, the grounding conductors and the surrounding region receive excessive stress, and are excessively deformed. As a result, the transmission characteristics of the triplate line will be degraded due to breakage of the grounding conductors or deformation of the grounding conductors and the surrounding region.